A variety of electrical switching applications desirably include the use of so-called double-break electrical contacts. Double break electrical contacts typically employ two spaced stationary contacts along with a movable contact that electrically bridges the two stationary contacts. The movable contact typically includes an electrically conductive, resilient bar or backing, typically made of metal, and mounting two spaced contacts that are aligned with the two stationary contacts. An actuator is employed to move the bar toward and away from the stationary contacts.
Applications include so-called "high power" applications and so-called "low voltage-low current" or "fidelity" applications. In a high power application, to achieve a long electrical life, a certain minimum cross-sectional area of the bar or backing of the movable contact is required. The cross-sectional area is selected so as to minimize heat rise when the bar is conducting a current between the two stationary contacts. Not untypically, the width of the movable contact bar is constrained and so, in effect, the minimum cross-sectional area of the bar translates into a minimum bar thickness.
In high power applications, oxide films and foreign particles that may lodge on the contacts and tend to separate the same are typically burnt away during switching and consequently, do not present a serious problem. On the other hand, a low voltage-low current applications, such oxide films or foreign particles may prevent the switching operation from completing itself when the contacts fail to make electrical contact with one another due to the presence of such films or particles. Consequently, ineffective or unreliable control functions may result. Consequently, so-called bifurcated contacts are frequently used in low voltage, low current applications.
By way of application, all rigid bodies resting against another rigid body contact at only three points. In non-bifurcated double-break contacts, the contact at one end of the bar will touch its respective stationary contact at two points, but the contact at the other end of the bar will touch its stationary contact at only one point. If there is a non-conductive oxide film or foreign particle at the single contact point, the bar will not electrically bridge the stationary contacts.
Flexible bodies, however, can come to rest against the rigid body at more than three points. Consequently, in conventional bifurcated, double break contacts, wherein four contacts are located on the bar, all four contacts will touch their respective stationary contacts. As a result, proper contact is lost only if both of the contacts at one end of the bar simultaneously land on areas of non-conductive, oxide film or on foreign particles. In order to achieve reliable contact, it is necessary that the split legs of the contact bar be sufficiently flexible, given the contact force supplied to the bar. The flexibility of the legs is, in turn, a function of the thickness of the backing and the length of the legs. Not infrequently, the movable bars are mounted on a post or alternatively, mounted between two posts. In either case, particularly when the bar is mounted on a post, considerable difficulty may be experienced in designing an effective bifurcated contact when (a) a minimum contact bar thickness is required to meet a "high power" specification; or (b) the length of the contact mounting legs on the bar is limited by the total length of the bar; or (c) the length of the backing legs is limited by the presence of a hole or notch for receiving a post or posts. Consequently, when it is desired to design a switching system employing bifurcated contacts and useful in both high power and in low voltage, low current applications, these factors must be considered.
The present invention is intended to provide a new and improved, double break switch construction which eliminates design problems in designing double break switch assemblies for use in both high power and low voltage-low current applications.